Two major immune abnormalities characterize SLE - 1) ability to make pathogenic autoantibodies (autoAb), and 2) persistent production of those Ab. In this proposal, we will test the hypothesis that structures in the V regions of H and L chains of pathogenic Ab, compared to non- pathogenic Ab, can be identified that account for pathogenicity. Such structures influence pathogenicity either by their antigen-binding properties, or their roles as T cell determinants that activate T-cell mediated upregulation. The hypothesis is based on our work showing that monoclonal Ab (mAb) derived from NZB/NZW F1 (BW) nephritic mice, which are IgG2a and IgG2b and have high affinity for double-stranded (ds) DNA, can be classified as pathogens or nonpathogens based on their ability to induce nephritis (GN) in healthy BALB/c mice. Some pathogens have interesting properties of binding proteins that link to nucleic acids (DNA/histone, polypeptides A and D of SnRNP). Pathogens and nonpathogens contain in their V/H regions several peptides that can activate T-cells from naive young BW mice; some sequences are common to several mAb; others may be unique to individual mAb. Using this information, we will perform experiments in 3 major areas as follows: 1. Alter the amino acid (AA) sequences in Ig H and/or L chains that are putative determinants of Ag reactivity, pathogenicity and T cell determinants; examine the effects on each of those properties compared to the unaltered "wild" Ig. This should permit identification of AA and AA sequences that contribute to pathogenicity. 2. Define the autoAb-derived peptides that serve as T-cell determinants, establishing their requisite AA structures, their MHC restriction, their prevalence in mouse Ig of various specificities, their dominance or crypticity, their ease of presentation by B cells of autoimmune mice, and the nature of the responding T cells. 3. By impairing the ability of BW B and T cells to interact via MHC/Ig-derived peptide/TCR complexes, prevent or ameliorate clinical lupus in BW mice. Two strategies will be investigated - induction of immune tolerance in T-cell help and/or B cells, and peptide blockade of TCR activation. The results of these experiments should provide new information regarding the pathogenesis of SLE, as well as novel therapeutic interventions.